Long-term effects of social stress exposure during adolescence in impulsivity : toward a new model of aggression




González Martínez, Lina Fernanda

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Adolescent male hamsters exposed to chronic social stress become themselves aggressive adults, evidenced by increased frequency of attacks and shorter latencies to attack opponents. Perhaps, this enhanced aggression is associated with a lack of impulse control, in particular with the ability to inhibit responses (i.e. action inhibition) and wait to respond (i.e. waiting impulsivity). Male golden hamsters were exposed daily to aggressive adults from postnatal day 28 to 42. Later, the animals were trained in conditioning chambers and tested in a Go-NoGo task to evaluate action inhibition. Overall, previously stressed hamsters were less likely to inhibit a conditioned lever pressing response during NoGo trials. These results show that animals exposed to social stress in early adolescence, have a decrease ability to withhold responses, which could possible explain why as adults, they have higher frequency of attacks. To test waiting impulsivity, animals learned to respond to a main house-light by nose-poking in any of two, adjacent illuminated ports in a modified version of a 5-choice-serial-reaction-time task (5-CSRTT). During testing, random and varying delays were introduced between the main house-light presentation and illumination of the ports, and premature nose-poking responses, (i.e. responses before the ports were illuminated) were considered an indicator of waiting impulsivity. As delays grew longer, animals performed more premature responses. However, previously stressed animals were 25% less likely to perform such actions by the longest delay. These studies show that early stress exposure enhanced the capacity to wait to perform a response, which is unrelated to aggression. Aspects of perseverance were tested in additional studies. In summary, chronic social stress exposure in early adolescence causes a variety of behavioral changes including enhanced aggression, decreased action inhibition and improved waiting impulsivity. This ambiguous relation between aggressive and impulsive behaviors suggests that perhaps there are multiple types of impulsive-aggression profiles related to different brain mechanisms. Thus, it is proposed that the concept of aggression should be reconsidered as a multidimensional construct mediating aspects of personality.



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